1. Field of the Invention
This invention relates generally to processes for producing olefin polymers. More specifically, this invention relates to a process for producing olefin polymers characterized by the use of a ctalyst which can provide highly stereoregular polymers in a high yield in the polymerization of .alpha.-olefins having not less than 3 carbon atoms.
2. Description of the Prior Art
Hitherto, it has been said that a catalyst system consisting of (i) a solid catalyst component having a titanium compound carried on a magnesium halide and (ii) an organoaluminum compound has a higher polymerization activity than conventional catalyst systems having no titanium compound carried thereon and may not need removal of catalyst residue from the resulting polymer. However, because the use of this carried catalyst causes low stereoregularity, it has been considered that the resulting polymer must be subjected to extraction procedure of so-called atactic polymers Recently, the stereoregularity owing to this carried catalyst has been considerably improved by the use of new co-catalyst systems. More specifically, it is known that a certain degree of highly active and highly stereoregular polymerization can be obtained by using, as polymerization additives, esters (U.S. Pat. No.4,226,741, Japanese Patent Laid-Open Publication No.157808/83, etc.) or phenyl- or alkyl-containing silicon compounds (European Patent Gazette E.P. No. 45975, E.P. No. 45976, E.P. No. 45977, etc.). Even by the use of these polymerization additives, however, it has been difficult to eliminate removal of catalyst residue and extraction process. Thus, further improvement has been desired in this respect.